“An Essay on the Principle of Population” written by Thomas Malthus in 1798 had a pessimistic point of view on large populations in the future world. However, world population had doubled in the past 50 years and reached 8 billion in November of 2022. Was Malthus wrong? To answer the above question, this course will first examine the pattern of demographic transition around the world. Specifically, the demographic statistics of global trends and country features will be investigated. Second, a basic concept of demographic transition will be introduced. We will focus the two factors that play important roles in forming a country’s demographic transition: fertility and mortality. In particular, we will pay attention to the phenomena of ultra-low fertilities in East Asian countries. Finally, we move to population aging and study its causes and possible policies.